The present invention relates to an information processing apparatus for recording and reproducing information on a plurality of kinds of optical recording media and an optical head device for use in the apparatus, and particularly to a technology for achieving both an enhancement of the light utilization efficiency of a first optical recording medium and an enhancement of beam spot quality pertaining to a second optical recording medium different in kind from the first optical recording medium in the information processing apparatus or the optical head device.
In a system using an optical recording medium such as compact disk (CD) and digital versatile disk (DVD), an optical head device (or optical pickup device) is used for reading information on the recording medium or recording desired information onto the recording medium.
For example, a two-wavelength type system capable of reproducing or recording information on two kinds of disks by use of two laser beams different in wavelength includes a laser diode (LD) for selective irradiation with two beams different in wavelength, a grating, a polarized beam splitter, a collimator, an objective lens, a holographic optical element (HOE), a photo-detector, or the like.
As for the light emission source composed by use of a laser diode, two LDs different in oscillation wavelength are used, for example in the case of a pickup device for CD recording and an exclusive use for DVD reproduction or in the case of a pickup device for CD recording and DVD recording.
In the case of CD recording (CD-R or the like), the magnification of an optical system including an objective lens and a collimator (the lateral magnification as viewed from the disk side) is ordinarily not more than 4, in view of the need to enhance the light utilization efficiency. On the other hand, in the case of reproduction or recording of information on a DVD, a magnification of not less than 6 is ordinarily used, since a lowering of the magnification broadens the light spot on the disk, possibly leading to degradation of the reproduction or recording performance.
Where an optical system including an objective lens and a collimator and using a two-wavelength type laser diode is used in common for a plurality of kinds of optical recording media, it is difficult with the conventional system to achieve both an enhancement of light utilization efficiency and an enhancement or maintenance of spot quality.
For example, where a system for CD-R recording and DVD recording or reproduction is composed by use of a two-wavelength type laser diode, in order to ensure DVD reproduction or recording performance it is necessary to increase the magnification of the optical system to a certain extent and, hence, to lower the light utilization efficiency pertaining to the CD-R, possibly resulting in that a sufficient recording speed on the CD-R cannot be obtained. On the contrary, in order to ensure a high recording speed by enhancing the light utilization efficiency pertaining to the CD-R, the magnification of the optical system is inevitably small, so that the DVD reproduction or recording performance may be degraded.
Thus, there has been the problem that an increase in the light utilization efficiency for one of the disks results in an adverse effect on the reproduction or recording performance for the other of the disks.